Sympathetic innervation of orbital targets normally is derived solely from the ipsilateral chain. However, unilateral superior cervical ganglionectomy of neonatal but not of juvenile or adult rats results in formation of an atypical contralateral pathway. The hypothesis to be tested is that the contralateral pathway derives from sprouting of sympathetic nerves innervating the anterior cerebral artery, and that outgrowth is prevented in older animals by local factors within the pathway and targets. The objectives of this study are to characterize contralateral outgrowth, and to elucidate mechanisms underlying temporal constraints. Specific aims are to: 1) determine the trajectory of outgrowth by a) immunohistochemical localization of endogenous markers (DBH, NPY), b) visualization of exogenous, anterogradely transported markers (WGA-HRP and/or DiI or 3H-leucine), and c) electrical stimulation of the presumptive intracranial pathways while recording target muscle contractions; 2) determine the derivation and target distributions of sprouting fibers by a) double labelling of cerebro-vascular and orbital structures (retrograde transport of Fluoro-Gold, RITC), and b) examining cerebro-vascular targets for the presence of varicosities of neurons labelled retrogradely by WGA-HRP injections of orbital target; 3) assess the role of competition with heterologous innervation in restricting outgrowth by a) parasympathetic denervation (pterygopalatine and ciliary ganglionectomy), b) sensory denervation (capsaicin), and c) combined parasympathetic and sensory denervation; 4) determine if age-dependent changes in pathway and target tissues induce or inhibit reinnervation by examining a) rate and extent of sympathetic sprouting into intraocular transplants of cerebrovascular and orbital target, and b) age-dependent changes in molecular constituents (laminin, NGF, glycosaminoglycans); 5) establish the neuropeptide content of neurons projecting to the ipsilateral and contralateral orbital targets, and assess the functional consequences of reinnervation of nonvascular smooth muscle by NPY-containing neurons. The significance of this study is that it will 1) elucidate mechanisms of enhanced outgrowth which lead to functional recovery of denervated targets, and 2) determine functional consequences of target reinnervation by sympathetic nerves displaying non-native neuropeptide profiles.